1. Field of the Invention
This invention relates to a machine and method for fabricating sheet metal sandwich structures and more particularly to such a machine and method which automatically fabricates such structures from flat metal foils.
2. Description of the Related Art
Sheet metal sandwich core panel structures are useful as backup material in the drilling of circuit boards. A method for using such backup material in this fashion is described in U.S. Pat. No. 4,269,549 issued May 26 1961 and assigned to LCOA, Laminating Company of America, the assignee of the present application. This type of structure also is used extensively as high strength to weight ratio panels in aircraft and in other applications.
Machines have been developed in the prior art for fabricating this type of structure. One such machine is described in G. W. Blessing U.S. Pat. No. 2,423,870, issued Jul. 15, 1947. In the machine described in this patent, a pair of outer metal foils or "skins" are joined to an inner sheet which is corrugated by being passed between a pair of corrugating rollers which are rotatably supported on support shafts. Adhesive is then applied to the surfaces of both the outer skins and the corrugated inner sheet and heat and pressure applied against the outer skins to bond the three foils together to form a composite structure.
While the basic steps followed by the Blessing machine are sound enough for forming many desired structures, it has been found that problems are presented in the mass production of such structures, particularly in situations where relatively wide panels are to be formed (of the order of 3 feet wide or greater). One of these problems is bending and deflection of the central panel during the corrugation step which results in a non-uniform often skewed core which is unsatisfactory particularly for applications for backup board such as described in the aforementioned U.S. Pat. No. 4,269,549. Further it has been found that unless special steps are taken to insure uniform heating of the panels that inadequate bonding of the structure is likely to occur. It is also important in achieving proper bonding that the foils be pressed against each other with uniform force over the entire surface thereof and that such force be precisely controlled to provide enough pressure to assure proper bonding of the structure but avoiding using so much force as to cause damage thereto.